Microwave and far infrared heating under reduced pressure

Abstract

Microwave and far infrared heating under reduced pressure is carried out on objects to be dried, concentrated, defrosted, roasted or sterilized by placing the objects in plate-shaped or tray-shaped object-holding jigs arranged on a shelf-type jig which is held motionless in a pressure reducing chamber during heating, wherein the provision of reflector plates, reflective frames, specific object-holding jigs and cutting methods are employed to achieve uniform heating.

Description

1. Field of the InventionThe present invention relates to a method and apparatus for heating objects using microwave and far infrared radiation under reduced pressure for the purpose of drying, concentrating, defrosting, roasting or sterilizing the objects.2. Description of the Prior ArtIn prior art heaters which utilize microwave and far infrared radiation for drying, concentrating, defrosting, roasting or sterilizing objects, uniform heating is achieved by placing the objects in a chamber on jigs such as plates or trays and shelf-type support jig for supporting the jigs which is rotated or on a conveyor which is moved, or the objects are stirred.However, prior art heaters having a rotatable jig for rotating objects to be heated are expensive and not suited for mass production due to the limited amount of objects that can be supported by the rotatable jig. Further, the scattering of powder and relatively light particles occurs in prior art heaters which stir objects to be dried, an...

AI Technical Summary

Benefits of technology

Now, in the embodiments of the present invention described in, the objects to be dried, concentrated, defrosted, roasted or sterilized are loaded on non-rotating plate-shaped or tray-shaped object-holding jigs stacked on a non-rotating shelf-type support jig placed at a prescribed position within the pressure reducing chamber, and because the objects are not agitated, there is no need for a rotation axle, whereby it becomes possible to reduce space loss, achieve a sufficient microwave depth penetration and significantly increase the surface area and holding capacity of the objects. Furthermore, the use of a lifting device makes it possible to easily and quickly load the object-holding jigs into the pressure reducing chamber, and because this speeds up the overall processing time, the use of a lifting device with the present invention is suited for mass production. Moreover, because the objects are not agitated, the present invention prevents the scattering of objects inside the pressure reducing chamber, and because this soiling of the inside of the pressure reducing chamber, the present invention makes it possible to improve maintenance and controllability. Further, the present invention is suited to achieve a high precision, uniform heating even when the objects are heated while held in place at a prescribed position instead of being moved on a conveyor or the like. Namely, in order to carry out a high precision control of heating, it is necessary to obtain the change in the reduced pressure level based on the balance of the water vapor content and the amount of exhaust of the vacuum pump, or the change in the water content of such exhaust, but in continuous supply methods such as the conveyor method in which objects having a high water content are continuously supplied, the objects that have just been supplied but not yet heated mix with objects that are near the completion of heating, and for this reason such systems do not display changes in the reduced pressure level according to a prescribed law, and this makes it difficult to obtain either the change in the reduced pressure level or the change in the water content of the exhaust to be used for control purposes. However, in the present invention, because only objects having roughly the same water content are present in the pressure reducing chamber, the balance between the amount of water vapor created and the amount of exhaust of the vacuum pump can be measured in accordance with a prescribed law, and this makes it possible to confirm that the change in the reduced pressure level and the amount of change in the reduced pressure level obey a prescribed law. Further, in the case where the amount of water vapor is measured, an extremely precise measurement of the increase thereof can be taken, and this makes it possible for the present invention to carry out high precision dryness level detection.

(6) When using high quality "clean"microwave radiation from a microwave emission source that is activated at the moment when electric current begins to flow and deactivated at the moment when electric current is cut off, the diffusion of such microwave radiation should be extremely effective, and this is effect is achieved by the present invention.

Problems solved by technology

However, prior art heaters having a rotatable jig for rotating objects to be heated are expensive and not suited for mass production due to the limited amount of objects that can be supported by the rotatable jig.

Further, the scattering of powder and relatively light particles occurs in prior art heaters which stir objects to be dried, and because such heaters are complex and expensive, they are not preferred.

Further, prior art heaters which move objects on a conveyor are quite suited for continuous production, but control of this type of heater is difficult.

Namely, because objects are continuously supplied, a mixture of objects having different water contents is created, and because this makes it difficult to accurately detect the completion of heating, a high production efficiency can not be achieved.

Further, because the accuracy in detecting the completion of heating is lowered, a control data base is required for each object when objects having different water contents are supplied at the time of each production, and this makes the control process extremely complicated.

Furthermore, such heating apparatuses are large in scale, and this together with the lower level of accuracy requires much time and cost to obtain conforming articles.

For the reasons given above, the use of heaters utilizing microwave and far infrared radiation under reduced pressure has not been widespread.

At this point, it should be mentioned that up to now it has been difficult to obtain uniform microwave heating and far infrared heating when the objects are not moved such as by rotation or agitation.

Further, prior art apparatuses and methods that continuously supply objects by moving them on top of a belt conveyor are suited for continuous production, but such arrangement makes it difficult to sufficiently control heating.

Namely, for continuous production to work with such prior art arrangement, the objects must be supplied and removed in order, and because this normally causes the immediately supplied objects having a high water content to mix with the objects that are near the completion of heating and have a low water content, the balance between the quantity of water vapor created and the quantity of exhaust removed by the vacuum pump does not obey a fixed law, and this leads to an irregular change in the reduced pressure level, which in turn makes it impossible to confirm the change in the reduced pressure level and the amount of change in the reduced pressure level in order to carry out high precision heating control.

Further, in the case where the shelf-type support jig is made of metal such as stainless steel or the like, if the end portions of the shelf-type support jig are too close to or come in contact with the walls inside the pressure reducing chamber, microwave radiation can cause discharges.

Now, because the resins are generally expensive, another embodiment uses object-holding jigs made of paper.

Further, the apparatus has paper object-holding jigs in which a coating or coated paper is provided on the surfaces of the object-holding jigs that come into contact with the objects in order to prevent the objects from sticking to such surfaces and thereby becoming difficult to remove.

Now, in case where square or rectangular object-holding jigs are used, it has been found that the objects present in the corner portions of such object-holding jigs receive more microwave radiation than the objects present in the central portion thereof, and for this reason it is easy for the objects in the central portion to receive an insufficient amount of heating compared to the amount of heating received by the objects in the corner portions.

Now, in case where solid objects are to be cut into smaller objects, if the smaller objects are produced with flat cut surfaces, the cut surface of one cut object will be in flush contact with the cut surface of another cut object if the cut objects are stacked together, and for this reason it will not be possible for microwave radiation to reach such cut surfaces, thus creating a hindrance to uniform heating.

(5) Up to now, the use of drying devices which utilize microwave radiation has not been widespread mainly due to the fact that, in addition to being expensive, such devices do not provide uniform heating and can not be used in mass production.

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